Modern petroleum drilling and production operations demand a great quantity of information relating to parameters and conditions downhole. Such information typically includes characteristics of the earth formations traversed by the wellbore, along with data relating to the size and configuration of the borehole itself. The collection of information relating to conditions downhole, which commonly is referred to as “logging”, can be performed by several methods.
In conventional oil well wireline logging, a probe (or “sonde”) housing formation sensors is lowered into the borehole after some or all of the well has been drilled. The formation sensors are used to determine certain characteristics, such as conductivity and resistivity, of the formations traversed by the borehole. The upper end of the sonde is attached to a conductive wireline that suspends the sonde in the borehole. Power is transmitted to the sensors and instrumentation in the sonde through the conductive wireline. Similarly, the instrumentation in the sonde communicates information to the surface by transmitting electrical signals through the wireline.
An alternative method of logging is the collection of data during the drilling process. Collecting and processing data during the drilling process eliminates the necessity of removing (“tripping”) the drilling assembly to insert a wireline logging device. It consequently allows the driller to make accurate modifications or corrections as needed to optimize performance while minimizing down time. Designs for measuring conditions downhole, including the movement and location of the drilling assembly contemporaneously with the drilling of the well, have come to be known as “measurement-while-drilling” techniques, or “MWD”. Similar techniques, concentrating more on the measurement of formation parameters, commonly have been referred to as “logging while drilling” techniques, or “LWD”. While distinctions between MWD and LWD may exist, the terms MWD and LWD often are used interchangeably. For the purposes of this disclosure, the term MWD will be used with the understanding that this term encompasses both the collection of formation parameters and the collection of information relating to the movement and position of the drilling assembly.
In both MWD and conventional wireline logging, as well as various other applications, the operating temperature experienced may be far in excess of normal surface conditions. Unfortunately, the operating temperature may exceed the specified ranges for some of the electrical components utilized in the downhole devices. Imaging devices that contain such components may operate unreliably in the downhole environment. Thus, what is needed in the art are imaging devices capable of operating reliably in high-temperature environments.
The following description has broad application. Each disclosed embodiment with accompanying discussion is meant only to be illustrative of that embodiment, and is not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.